Billionaire energy tycoon Dan Duncan, who founded one of the largest energy services companies in the U.S., died at his Houston home Sunday, according to the Associated Press. He was 77. Duncan was chairman of the company that manages Enterprise Products Partners LP, a midstream energy giant with more than 48,000 miles of natural gas, petrochemical and crude oil pipelines and 25 natural gas processing plants. The company focuses its services in the processing, storage and transportation sectors within the oil and gas industry. Duncan co-founded Enterprise Products Company in 1968 and took Enterprise Products Partners public in July 1998. This year, he ranked 74th on Forbes'' worldwide list of billionaires, with an estimated net worth of $9 billion. He was Houston''s wealthiest resident, according to the list.